<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    首页
    <button>发送一个请求</button>
    <script>
        let btn = document.querySelector('button')
        btn.onclick = function () {
            let xhr = new XMLHttpRequest()
            xhr.open('get', '/a', true)
            xhr.send()
            xhr.onreadystatechange = function () {
                if (xhr.readyState === 4 && xhr.status === 200) {
                    console.log(xhr.responseText);

                }
            }
        }


    </script>
</body>

</html>